> On HN, who are you going to convince and what for?

There are plenty of things bots would be useful for here, just as they are on any discussion forum. Mainly, whenever someone wants to steer the discussion away from or towards a certain topic. This could be useful to protect against bad PR, to silence or censor certain topics from the outside by muddying up the discussion, or to influence the general mindset of the community. Many people trust comments that seem to come from an expert, so pretending to be one, or hijacking the account of one, gets your point across much more easily.

I wouldn't be so sure that bots aren't already dominating here. It's just that it's frowned upon to discuss such things in the comments section, and we don't really have a way of verifying it in any case.